Additive, electrolyte for lithium secondary battery including additive, and lithium secondary battery

Abstract

To provide an electrolyte additive for a lithium secondary battery that improves the life characteristics while suppressing an increase in resistance and gas generation in the lithium secondary battery at high temperature.SOLUTION: The present invention relates to an additive, an electrolyte for a lithium secondary battery including the additive, and a lithium secondary battery, the additive is represented by the following chemical formula 1. (In chemical formula 1, L1 is a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, and R1 to R4 are each independently a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.)SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an additive, an electrolyte for a lithium secondary battery containing the additive, and a lithium secondary battery. [Background technology]

[0002] Recently, the demand for high-energy-density, high-capacity secondary batteries has been growing rapidly with the rapid spread of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles. This has led to active research and development into improving the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a positive electrode, a negative electrode, and an electrolyte, each of which includes an active material capable of intercalating and deintercalating lithium ions, and produces electrical energy through oxidation and reduction reactions that occur when lithium ions are intercalated / deintercalated from the positive electrode and the negative electrode.

[0004] Recently, one of the development directions of lithium secondary batteries is to improve their high-temperature characteristics. Generally, lithium secondary batteries may have problems such as increased resistance, gas generation, and reduced lifespan at high temperatures. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-299542 A Summary of the Invention [Problem to be solved by the invention]

[0006] An embodiment of the present invention provides an electrolyte additive for a lithium secondary battery that improves the life characteristics while suppressing an increase in resistance and gas generation of the lithium secondary battery at high temperatures. [Means for solving the problem]

[0007] An embodiment of the present invention provides an electrolyte additive for a lithium secondary battery represented by the following Chemical Formula 1:

[0008] [Chemical formula 1] [ka]

[0009] In chemical formula 1, L 1 is a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, R 1 ~R 4 each independently represents a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

[0010] An embodiment of the present invention provides an electrolyte for a lithium secondary battery, comprising the electrolyte additive for a lithium secondary battery.

[0011] An embodiment of the present invention provides a lithium secondary battery including the above-mentioned electrolyte for lithium secondary batteries. Effect of the Invention

[0012] The electrolyte additive for lithium secondary batteries according to the present invention can suppress metal elution from the positive electrode active material at high temperatures, and can improve the life characteristics of the lithium secondary battery while suppressing an increase in resistance and gas generation. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. [Diagram 3] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. [Figure 4] FIG. 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail, but they are given by way of example only and are not intended to limit the present invention, which is defined only by the scope of the following claims.

[0015] Unless otherwise specified in this specification, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between.

[0016] Unless otherwise specified herein, the singular can also include the plural. At the same time, unless otherwise specified, "A or B" means "including A, including B, or including A and B."

[0017] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0018] Unless otherwise specified in this specification, an "alkyl group" means an alkyl group having 1 to 20 carbon atoms, an "alkenyl group" means an alkenyl group having 2 to 20 carbon atoms, a "cycloalkenyl group" means a cycloalkenyl group having 3 to 20 carbon atoms, a "heterocycloalkenyl group" means a heterocycloalkenyl group having 3 to 20 carbon atoms, an "aryl group" means an aryl group having 6 to 20 carbon atoms, an "arylalkyl group" means an arylalkyl group having 6 to 20 carbon atoms, an "alkylene group" means an alkylene group having 1 to 20 carbon atoms, an "arylene group" means an arylene group having 6 to 20 carbon atoms, an "alkylarylene group" means an alkylarylene group having 6 to 20 carbon atoms, a "heteroarylene group" means a heteroarylene group having 3 to 20 carbon atoms, and an "alkoxyylene group" means an alkoxyylene group having 1 to 20 carbon atoms.

[0019] Unless otherwise specified in this specification, "substituted" means that at least one hydrogen atom is replaced with a halogen atom (F, Cl, Br, I), a hydroxy group, an alkoxy group having 1 to 20 carbon atoms, a nitro group, a cyano group, an amino group, an imino group, an azide group, an amidino group, a hydrazino group, a hydrazono group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, an ether group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, an alkyl group having 1 to 20 carbon atoms, It means being substituted with an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, a cycloalkenyl group having 3 to 20 carbon atoms, a cycloalkynyl group having 3 to 20 carbon atoms, a heterocycloalkyl group having 2 to 20 carbon atoms, a heterocycloalkenyl group having 2 to 20 carbon atoms, a heterocycloalkynyl group having 2 to 20 carbon atoms, a heteroaryl group having 3 to 20 carbon atoms, or a combination thereof.

[0020] Unless otherwise defined in the chemical formulas herein, when no chemical bond is drawn at a position where a chemical bond should be drawn, this means that a hydrogen atom is bonded at that position.

[0021] (Electrolyte additive for lithium secondary batteries) One embodiment provides an electrolyte additive for lithium secondary batteries (hereinafter, sometimes simply referred to as "additive") represented by the following chemical formula 1:

[0022] [Chemical formula 1] [ka]

[0023] The electrolyte additive for lithium secondary batteries according to one embodiment contains phosphate groups and aryl groups symmetrically, and is oxidized and decomposed on the surface of the positive electrode to form a highly stable and heat-resistant SEI film. The SEI film formed on the surface of the positive electrode can suppress metal elution from the positive electrode active material, and can improve the life characteristics of the lithium secondary battery while suppressing an increase in resistance and gas generation.

[0024] The explanation of Chemical Formula 1 showing the additive is as follows:

[0025] L 1 is a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms.

[0026] For example, L 1 may be a substituted or unsubstituted alkylene group having 1 to 3 carbon atoms.

[0027] R 1 ~R 4 each independently represents a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

[0028] For example, R 1 ~R 4 may all be phenyl groups.

[0029] Chemical formula 1 may be represented by the following Chemical formula 1-1.

[0030] [Chemical formula 1-1] [ka]

[0031] In chemical formula 1-1, L 1 The definition is as described above.

[0032] Representative examples of Chemical Formula 1 are represented by the following Chemical Formulae 1-1-1 to 1-1-3.

[0033] [Chemical formula 1-1-1] [ka]

[0034] [Chemical formula 1-1-2] [ka]

[0035] [Chemical formula 1-1-3] [ka] .

[0036] (Electrolyte for lithium secondary batteries) One embodiment provides an electrolyte solution for a lithium secondary battery (hereinafter, may be simply referred to as "electrolyte solution") comprising a non-aqueous organic solvent, a lithium salt, and an additive represented by the following chemical formula 1.

[0037] [Chemical formula 1] [ka]

[0038] The electrolyte for a lithium secondary battery according to an embodiment includes the additive described above. The additive contained in the electrolyte can suppress metal elution from the positive electrode active material at high temperatures and can improve the life characteristics of the lithium secondary battery while suppressing an increase in resistance and gas generation.

[0039] The additive may be contained in an amount of 0.05 to 3 wt %, 0.05 to 2 wt %, or 0.05 to 1 wt % relative to 100 wt % of the electrolyte solution. Within the above range, the additive is oxidized and decomposed on the positive electrode surface to form an SEI coating that is highly stable and heat resistant.

[0040] (Non-aqueous organic solvent) The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0041] The non-aqueous organic solvent may be a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0042] Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0043] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0044] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0045] (Lithium salts) Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in the battery to enable basic lithium secondary battery operation and facilitate the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0046] (lithium secondary battery) One embodiment provides a lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte including a non-aqueous organic solvent, a lithium salt, and an additive represented by the following Chemical Formula 1:

[0047] [Chemical formula 1] [ka]

[0048] The lithium secondary battery according to one embodiment includes an electrolyte solution containing the additive described above. The additive contained in the electrolyte solution can suppress metal elution from the positive electrode active material at high temperatures, and can improve the life characteristics of the lithium secondary battery while suppressing an increase in resistance and gas generation.

[0049] (Cathode active material) The positive electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound). Specifically, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0050] The composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0051] As an example, Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05), Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05), Li a Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2), Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2), Li a Ni b Co c L 1 d G e O2 (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1), Li a NiG bO2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a CoG b O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn 1-b G b O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn2G b O4 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5), Li (3-f) Fe2(PO4)3(0≦f≦2);Li a Any one of the compounds represented by the chemical formula FePO4 (0.90≦a≦1.8) can be used.

[0052] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0053] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of metals excluding lithium in a lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0054] The positive electrode active material may include a lithium nickel-based composite oxide represented by the following chemical formula 11.

[0055] [Chemical formula 11] Li a1 Nix1 M 1 y1 M 2 z1 O 2-b1 X b1

[0056] In Chemical Formula 11, 0.9≦a1≦1.2, 0.7≦x1≦1, 0≦y1≦0.3, 0≦z1≦0.1, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M. 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0057] In Chemical Formula 11, 0.75≦x1≦1, 0≦y1≦0.28, and 0≦z1≦0.08, or 0.85≦x1≦1, 0≦y1≦0.15, and 0≦z1≦0.15, or 0.9≦x1≦1, 0≦y1≦0.1, and 0≦z1≦0.1.

[0058] In addition, the positive electrode active material may include a lithium nickel-based composite oxide represented by the following Chemical Formula 12. The compound represented by the following Chemical Formula 12 may be a lithium nickel cobalt-based composite oxide.

[0059] [Chemical formula 12] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0060] In chemical formula 12, 0.9≦a2≦1.8, 0.7≦x2<1, 0 <y2≦0.2、0≦z2≦0.2、0.9≦x2+y2+z2≦1.1、および0≦b2≦0.1であり、M 3is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0061] In Chemical Formula 12, 0.75≦x2≦0.99, 0≦y2≦0.15, and 0≦z2≦0.15, or 0.85≦x2≦0.99, 0.01≦y2≦0.15, and 0.01≦z2≦0.15, or 0.9≦x2≦0.99, 0.01≦y2≦0.1, and 0.01≦z2≦0.1.

[0062] In addition, the positive electrode active material may include a lithium nickel-based composite oxide represented by the following Chemical Formula 13. The compound of the following Chemical Formula 13 may be lithium nickel-cobalt-aluminum oxide or lithium nickel-cobalt-manganese oxide.

[0063] [Chemical formula 13] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0064] In Chemical Formula 13, 0.9≦a3≦1.8, 0.7≦x3≦0.98, 0.01≦y3≦0.19, 0.01≦z3≦0.19, 0≦w3≦0.19, 0.9≦x3+y3+z3+w3≦1.1, and 0≦b3≦0.1; M 4 is one or more elements selected from the group consisting of Al and Mn, 5 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0065] In Chemical Formula 13, 0.75≦x3≦0.98, 0≦y3≦0.16, and 0≦z3≦0.16, or 0.85≦x3≦0.98, 0.01≦y3≦0.14, 0.01≦z3≦0.14, and 0≦w3≦0.14, or 0.9≦x3≦0.98, 0.01≦y3≦0.09, 0.01≦z3≦0.09, and 0≦w3≦0.09.

[0066] In addition, the positive electrode active material may include a lithium nickel-based composite oxide represented by the following Chemical Formula 14. The compound of the following Chemical Formula 14 may be a cobalt-free lithium nickel-manganese-based oxide.

[0067] [Chemical formula 14] Li a4 Ni x4 Mn y4 M 6 z4 O 2-b4 X b4

[0068] In chemical formula 14, 0.9≦a2≦1.8, 0.7≦x4<1, 0 <y4≦0.3、0≦z4≦0.1、0.9≦x4+y4+z4≦1.1、および0≦b4≦0.1であり、M 6 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0069] Cobalt-free lithium nickel manganese oxides have a strong structural instability, so that under high voltage and / or high temperature conditions, the structure collapses and the transition metal (e.g., Ni) dissolves, dramatically increasing the stability and lifespan of the lithium secondary battery.

[0070] However, the additive for lithium secondary batteries according to one embodiment, even when used in combination with a cobalt-free lithium nickel-manganese-based oxide, can suppress the structural collapse of the cobalt-free lithium nickel-manganese-based oxide under high voltage and / or high temperature conditions, and can improve the stability and life characteristics of the lithium secondary battery.

[0071] (positive electrode) The positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material, and may further include a binder and / or a conductive material.

[0072] As an example, the positive electrode can further include an additive that can act as a sacrificial positive electrode.

[0073] The content of the positive electrode active material may be 90% by weight to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, and the contents of the binder and conductive material may each be 0.5% by weight to 5% by weight relative to 100% by weight of the positive electrode active material layer.

[0074] The binder serves to make the positive electrode active material particles adhere well to each other and to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0075] The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause chemical changes in the battery that is constructed and is electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes, metal-based materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, or silver, conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0076] The current collector may be made of Al, but is not limited to this.

[0077] (Negative electrode active material) The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0078] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, or calcined coke.

[0079] As the alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0080] As a substance that can be doped and de-doped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0081] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0082] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0083] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0084] (Negative electrode) The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or a conductive material.

[0085] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0086] The binder serves to adhere the negative electrode active material particles to each other and to the current collector well. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0087] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymers, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0088] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0089] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used.

[0090] The dry binder may be a polymeric material capable of being fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0091] The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause chemical changes in the battery that is constructed and is electronically conductive can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes, metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, or silver, conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0092] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0093] (Separator) Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multi-layer film of two or more layers of these may be used, and it is of course possible to use a mixed multi-layer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0094] The separator can include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0095] The porous substrate may be a polymer membrane formed from any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0096] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0097] The inorganics can include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0098] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be laminated.

[0099] (lithium secondary battery) Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, and other types according to their shapes. FIGS. 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment, in which FIG. 1 shows a cylindrical battery, FIG. 2 shows a square battery, and FIGS. 3 and 4 show a pouch battery. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 between a positive electrode 10 and a negative electrode 20, with a separator 30 interposed therebetween, and a case 50 in which the electrode assembly 40 is built in. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). As shown in FIG. 1, the lithium secondary battery 100 can include a sealing member 60 that seals the case 50. In addition, in FIG. 2, the lithium secondary battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0100] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, but the present invention is not limited thereto.

[0101] Examples and comparative examples of the present invention will be described below. However, the examples described below are merely examples of the present invention, and the present invention is not limited to the examples described below. EXAMPLES

[0102] (Synthesis Example 1: Compound represented by chemical formula 1-1-1) 1,2-Bis(diphenylphosphino)ethane (0.5 mmol, 2.5 mg) and hydrogen peroxide (3.0 mmol) were added dropwise to a Schlenk flask containing 100 ml of methylene chloride, and the mixture was stirred at 50°C for 24 hours. The precipitate was then filtered, and the resulting compound was dissolved in a small amount of acetone to obtain a solution. The solution was slowly added dropwise to 500 ml of methylene chloride using a dropping funnel, and the resulting reaction product was filtered, purified, and then vacuum dried to obtain the compound represented by chemical formula 1-1-1.

[0103] [Chemical formula 1-1-1] [ka]

[0104] (H NMR(300MHz): δ=2.49, 2.50(4H, CH2P); 7.42(t, 3JHH=7.5Hz, 8H); 7.47(t, 3JHH=7.4Hz, 4H); 7.68(dd, 3JHH=7.5Hz, 3JHP=12.0Hz, 8H))

[0105] <Example 1> (1) Electrolyte production 1.15M LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 2:1:7, and 0.5 wt% of an additive represented by chemical formula 1-1-1 was added to prepare an electrolyte.

[0106] Here, the content of the additive in the composition of the electrolyte solution in "wt %" is based on the entire electrolyte solution (lithium salt + non-aqueous organic solvent + additive) being 100 wt %.

[0107] (2) Manufacture of lithium secondary batteries LiNi as the positive electrode active material 0.75 Mn 0.23 Al 0.02 O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:3:1, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0108] The positive electrode active material slurry was coated on an aluminum foil having a thickness of 15 μm, dried at 100° C., and pressed to prepare a positive electrode.

[0109] A mixture of artificial graphite and Si-C composite in a weight ratio of 93:7 was used as the negative active material, and the negative active material was mixed with styrene-butadiene rubber binder and carboxymethyl cellulose in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative active material slurry.

[0110] The Si-C composite used was one in which a core containing artificial graphite and silicon particles was coated on the surface of the core with coal-based pitch.

[0111] The negative electrode active material slurry was coated on a copper foil having a thickness of 10 μm, dried at 100° C., and pressed to prepare a negative electrode.

[0112] The prepared positive and negative electrodes were assembled with a 10 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte was injected to prepare a lithium secondary battery.

[0113] <Example 2> An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the content of the additive was changed to 1 wt %.

[0114] <Example 3> An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the content of the additive was changed to 2 wt %.

[0115] <Example 4> The positive electrode active material is LiNi 0.9 Co 0.05 Al 0.05 An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that O2 was used.

[0116] <Example 5> An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 4, except that the content of the additive was changed to 1 wt %.

[0117] <Example 6> An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 4, except that the content of the additive was changed to 2 wt %.

[0118] <Comparative Example 1> An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that no additive was added.

[0119] <Comparative Example 2> An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a compound represented by the following formula A (CAS No. 1663-45-2, manufactured by Aldrich) was used instead of the additive represented by formula 1-1-1.

[0120] [Chemical formula A] [ka]

[0121] <Comparative Example 3> An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a compound represented by the following formula B (CAS No. 23936-60-9, manufactured by Aldrich) was used instead of the additive represented by formula 1-1-1.

[0122] [Chemical formula B] [ka]

[0123] <Comparative Example 4> The positive electrode active material is LiNi 0.9 Co 0.05 Al 0.05 An electrolyte and a lithium secondary battery were manufactured in the same manner as in Comparative Example 1, except that O2 was used.

[0124] <Comparative Example 5> The positive electrode active material is LiNi 0.9 Co 0.05 Al 0.05 An electrolyte and a lithium secondary battery were manufactured in the same manner as in Comparative Example 2, except that O2 was used.

[0125] <Comparative Example 6> The positive electrode active material is LiNi 0.9 Co 0.05 Al 0.05 An electrolyte and a lithium secondary battery were manufactured in the same manner as in Comparative Example 3, except that O2 was used.

[0126] (Evaluation example 1: High temperature storage characteristic evaluation) (1) DCIR Increase Rate For the lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 6, the initial direct current resistance (DCIR) was measured using the ΔV / ΔI (change in voltage / change in current) value. Next, the maximum energy state inside the battery was set to a fully charged state (SOC 100%), and the battery was stored in this state at high temperature (60°C) for 30 days, after which the direct current resistance was measured. The DCIR increase rate (%) was calculated using the following formula 1, and the results are shown in Table 1 below.

[0127] [Formula 1] DCIR increase rate = (DCIR after 30 days / initial DCIR) x 100

[0128] [Table 1]

[0129] (2) Amount of gas generated The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 were set to a fully charged state (SOC 100%) as the maximum energy state inside the battery. After storing the batteries in this state at high temperature (60°C) for one or seven days, the amount of gas generated was evaluated, and the results are shown in Table 2 below.

[0130] The amount of gas generated was determined by measuring the volume change before and after high-temperature storage, and converting this into mass change using Archimedes' law.

[0131] [Table 2]

[0132] (Evaluation example 2: Evaluation of charge / discharge characteristics at high temperatures) The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to 200 charge / discharge cycles under the conditions of 45°C, 0.33C charge (CC / CV, 4.45V, 0.025C cut-off) / 1.0C discharge (CC, 2.5V cut-off), and then the capacity retention rate was calculated using the following formula 2.

[0133] [Formula 2] Capacity retention rate = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) × 100

[0134] [Table 3]

[0135] (Overall) According to Table 1, in the lithium secondary batteries of Examples 1 to 6, the increase in resistance at high temperatures was suppressed compared to the lithium secondary batteries of Comparative Examples 1 to 6.

[0136] Moreover, according to Tables 2 and 3, the lithium secondary batteries of Examples 1 to 3 suppressed gas generation at high temperatures and had improved life characteristics, compared with the lithium secondary batteries of Comparative Examples 1 to 3.

[0137] From these findings, it was found that the additive according to one embodiment suppresses metal elution from the positive electrode active material at high temperatures, and improves the life characteristics while suppressing an increase in resistance and gas generation in the lithium secondary battery.

[0138] In addition, it has been found that the additive according to one embodiment, when used in combination with a cobalt-free lithium nickel manganese oxide, suppresses the structural collapse of the cobalt-free lithium nickel manganese oxide even under high voltage and / or high temperature conditions.

[0139] Although the above describes a preferred embodiment of the present invention, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the attached drawings, which of course also fall within the scope of the present invention. [Explanation of symbols]

[0140] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing material 70 Electrode tab 71 Positive tab 72 Negative tab

Claims

1. An electrolyte additive for a lithium secondary battery represented by the following chemical formula 1: [Chemical formula 1] 【Chemistry 1】 In the above Chemical Formula 1, L １ is a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, R １ ~R ４ are each independently a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

2. L １ The electrolyte additive for lithium secondary batteries according to claim 1, wherein is a substituted or unsubstituted alkylene group having 1 to 3 carbon atoms.

3. R １ ~R ４ The electrolyte additive for lithium secondary batteries according to claim 1 , wherein all of the groups are phenyl groups.

4. The electrolyte additive for a lithium secondary battery according to claim 1, wherein the chemical formula 1 is represented by the following chemical formula 1-1: [Chemical formula 1-1] 【Chemistry 2】 。

5. The electrolyte additive for a lithium secondary battery according to claim 1, wherein the chemical formula 1 is represented by any one of the following chemical formulas 1-1-1 to 1-1-3: [Chemical formula 1-1-1] 【Chemistry 3】 [Chemical formula 1-1-2] 【Chemistry 4】 [Chemical formula 1-1-3] 【Chemistry 5】 。

6. A non-aqueous organic solvent; A lithium salt; An electrolyte for a lithium secondary battery comprising an additive represented by the following chemical formula 1: [Chemical formula 1] 【Chemistry 6】 In the above Chemical Formula 1, L １ is a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, R １ ~R ４ are each independently a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

7. 7. The electrolyte for lithium secondary batteries according to claim 6, wherein the additive is contained in an amount of 0.05 to 3% by weight based on 100% by weight of the electrolyte for lithium secondary batteries.

8. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; A lithium secondary battery comprising: an electrolyte solution containing a non-aqueous organic solvent, a lithium salt, and an additive represented by the following chemical formula 1: [Chemical formula 1] 【Chemistry 7】 In the above Chemical Formula 1, L １ is a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, R １ ~R ４ are each independently a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

9. The lithium secondary battery according to claim 8 , wherein the positive electrode active material comprises a lithium nickel-based composite oxide.

10. The lithium secondary battery according to claim 9, wherein the positive electrode active material comprises a lithium nickel-based composite oxide represented by the following chemical formula 11: [Chemical formula 11] Li ａ１ Ni ｘ１ M １ ｙ１ M ２ ｚ１ O ２－ｂ１ X ｂ１ In the above Chemical Formula 11, 0.9≦a1≦1.2, 0.7≦x1≦1, 0≦y1≦0.3, 0≦z1≦0.1, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1, M １ and M. ２ are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr; X is one or more elements selected from the group consisting of F, P and S.

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